The incidence and effect of exposure to toxic substances by humans and other animals via food, water, and air is of critical importance to our survival. Within the general class of toxic substances, the detection of small molecular weight (1,000 daltons or less) mutagens and/or carcinogens such as aflatoxins, fluoranthene, nitropyrene, nitrofluoranthene, nitrochrysene, and aminobiphenyls have become especially important. In particular, non-invasive screening procedures for assessing the exposure of humans to substances such as aflatoxins require the ability to quantify both the toxin and its metabolites, especially covalent adducts formed with DNA and proteins, in body fluids such as serum and urine.
Aflatoxins are a typical example of the toxic and carcinogenic compounds within this class. Aflatoxins are secondary fungal metabolites, mycotoxins, which are produced by Aspergillus flavus and Aspergillus parasiticus and are structurally a group of substituted coumarins containing a fused dihydrofurofuran moiety. Aflatoxins occur naturally in peanuts, peanut meal, cottonseed meal, corn, dried chili peppers and the like; however the growth of the mold itself does not predict the presence or levels of the toxin because the yield of aflatoxin depends on growth conditions as well as the genetic requirements of the species. A variety of aflatoxins--types B.sub.1, B.sub.2, G.sub.1, G.sub.2, M.sub.1 and M.sub.2 --have been isolated and characterized. Aflatoxin B.sub.1 (hereinafter "AFB.sub.1 ") is the most biologically potent of these compounds and has been shown to be toxic, mutagenic and carcinogenic in many animal species. This mycotoxin is a frequent contaminant of the human food supply in many areas of the world and is statistically associated with increased incidence of human liver cancer in Asia and Africa in particular [Busby et al., in Food-Born Infections and Intoxications (Riemann and Bryan, Editors) Second Edition, Academic Press, Inc., 1979, pp. 519-610; Wogan, G. N. Methods Cancer Res. 7:309-344 (1973)].
AFB.sub.1 also forms covalently linked adducts with guanine in DNA after oxidative metabolism to a highly reactive 2,3 - exo-epoxide, the major aduct product being 2,3 - dihydro - 2 - (N.sup.7 -guanyl) - 3-hydroxy - aflatoxin B.sub.1 (hereinafter identified as "AFB.sub.1 -N.sup.7 -Gua") [Lin et al., Cancer Res. 37:4430-4438 (1977); Essigman et al., Proc. Natl. Acad. Sci. USA 74:1870-1874 (1977); Martin et al., Nature (London) 267:863-865 (1977)]. The AFB.sub.1 -N.sup.7 -Gua adduct and its putative derivatives [2,3-dihydro - 2-(N.sup.5 -formyl-2',5',6' -triamino - 4'-oxo' N.sup.5 -pyrimidyl) - 3-hydroxy - aflatoxin B.sub.1 ] (hereinafter "AF-N.sup.7 -Gua") have been identified in a wide variety of tissues and systems such as rat liver in vivo, cultured human bronchus and colon, and human lung cells in culture after acute or chronic administration [Haugen et al., Proc. Natl. Acad. Sci. USA 78:4124-4127 (1981)].
Some investigations regarding quantitation of aflatoxin B.sub.1 and its metabolites including its DNA adduct have been conducted using immunological techniques and monoclonal antibodies [Hertzog et al., Carcinogensis 3:825-828 (1982); Groopman et al., Cancer Res. 42:3120-3124 (1982); Haugen et al., Proc. Natl. Acad. Sci. USA 78: 4124-4127 (1981)]. Similar research has been conducted utilizing immunological techniques and reagents for other low molecular weight toxins found in our environment [Johnson et al., J. Analyt. Toxicol. 4:86-90 (1980); Sizaret et al., J.N.C.I. 69:1375-1381 (1982); Hu et al., J. Food Prot. 47:126-127 (1984); and Chu, J. Food Prot. 47:562-569 (1984)]. Nevertheless, insofar as is presently known, the development of a general non-invasive screening procedure for assessing the exposure of humans and animals to such environmentally occuring carcinogens has not been achieved.